The invention relates to a continuous process for the polymerisation and copolymerisation of .alpha.-olefines in bulk, that is to say in the absence of diluents or suspending agents, by means of organo-metallic mixed catalysts or catalysts containing chromium oxide or molybdenum oxide, using self-stripping twin-screw or multi-screw reactors.
The known large-scale industrial processes for the polymerisation and copolymerisation of .alpha.-olefines in the medium and low pressure range by means of organo-metallic mixed catalysts or catalysts containing chromium oxide or molybdenum oxide are in general carried out in the presence of a liquid diluent or suspending agent which must be worked up, and recycled to the process, after separating off the polymer and residual monomer. The recycling of the diluent or suspending agent requires a great deal of technological effort and is very expensive because of the unavoidable losses of diluents or suspending agents which it entails. The same remarks also apply to the recycling of the residual monomer, the amounts of which are normally considerable. In these processes the polymer is in general obtained, after isolation and drying, in a very finely divided and pulverulent form and must normally be brought to a marketable form by subsequent processing in granulating extruders.
Processes for the gas phase polymerisation of .alpha.-olefines (see Chem. Eng. Sept. 18, 1972, pages 104-105, and Chem. Eng. Oct. 16, 1972, page 62), in which the monomer, which is treated as recycle gas, assumes the role of a diluent, are also known. In these, the amount of recycle gas must be many times the amount of fresh gas. Both the isolation of the finely divided polymer from a very large amount of gas and its recycling, cooling and purification demand expensive process steps. Here again the polymer which is obtained in a very finely divided form must be converted to a desired form, for example by subsequent processing in granulating extruders.
DT-AS (German Published Specification) 1,247,657 describes a process which is carried out in the presence of preformed polymer as a diluent. The reactors mentioned are special autoclaves, pressure-resistant kneaders or single-screw extruders of which the screw shaft has an axial bore through which a part of the polymer melt is recycled from the output end to the feed zone of the extruder.
The known processes have the disadvantage that they take place in the presence of a diluent, as a result of which the rate of reaction is lowered and a large reaction volume is required. This necessarily leads to a marked worsening of the space-time yield of the reaction, that is to say to a poorer degree of utilisation of the reaction space. A further disadvantage of the known reactions is that polymer deposits in reactors and in working-up vessels are unavoidable and must periodically be removed, at considerable cost.